This invention relates generally to the liquefaction of industrial gas and, more particularly, to the liquefaction of industrial gas using a multiple circuit liquefier.
The liquefaction of industrial gas is a power intensive operation. Typically the industrial gas is liquefied by indirect heat exchange with a refrigerant. Such a system, while working well for providing refrigeration over a relatively small temperature range from ambient, is not as efficient when refrigeration over a large temperature range, such as from ambient to a cryogenic temperature, is required. This inefficiency may be addressed by using more than one refrigeration circuit to get the requisite cryogenic condensing temperature. However, such systems require a significant power input in order to achieve the desired results and/or require complicated and costly heat exchanger designs and phase separators in the circuit.
Accordingly, it is an object of this invention to provide a multiple circuit arrangement whereby industrial gas may be brought from ambient temperature to a colder temperature, especially to a cryogenic liquefaction temperature, which is less complicated than heretofore available multiple circuit systems while operating with a relatively low power input requirement.
The above and other objects, which will become apparent to those skilled in the art upon a reading of this disclosure, are attained by the present invention, one aspect of which is:
A method for cooling industrial gas comprising:
(A) compressing a gaseous azeotropic mixture, and condensing the compressed azeotropic mixture;
(B) expanding a first portion of the condensed azeotropic mixture to generate refrigeration, and vaporizing the refrigeration bearing azeotropic mixture first portion by indirect heat exchange with the compressed azeotropic mixture to effect the said condensation of the compressed azeotropic mixture;
(C) subcooling a second portion of the condensed azeotropic mixture and expanding the subcooled azeotropic mixture second portion to generate high level refrigeration;
(D) vaporizing the high level refrigeration bearing azeotropic mixture second portion by indirect heat exchange with compressed refrigerant fluid to provide cooled, compressed refrigerant fluid;
(E) expanding the cooled compressed refrigerant fluid to generate low level refrigeration; and
(F) warming the low level refrigeration bearing refrigerant fluid by indirect heat exchange with industrial gas to cool the industrial gas.
Another aspect of the invention is:
A method for cooling industrial gas comprising:
(A) compressing a gaseous azeotropic mixture, condensing the compressed azeotropic mixture, and expanding the compressed condensed azeotropic mixture to generate high level refrigeration;
(B) vaporizing the high level refrigeration bearing azeotropic mixture by indirect heat exchange with compressed refrigerant fluid to provide cooled compressed refrigerant fluid;
(C) expanding the cooled compressed refrigerant fluid to generate low level refrigeration; and
(D) warming the low level refrigeration bearing refrigerant fluid by indirect heat exchange with industrial gas to cool the industrial gas.
As used herein, the term xe2x80x9cexpansionxe2x80x9d means to effect a reduction in pressure.
As used herein, the term xe2x80x9cindustrial gasxe2x80x9d means nitrogen, oxygen, argon, hydrogen, helium, carbon dioxide, carbon monoxide, krypton, xenon, neon, methane and other hydrocarbons having up to 4 carbon atoms, and fluid mixtures comprising one or more thereof.
As used herein, the term xe2x80x9ccryogenic temperaturexe2x80x9d means a temperature of 150xc2x0 K or less.
As used herein, the term xe2x80x9crefrigerationxe2x80x9d means the capability to reject heat from a subambient temperature system to the surrounding atmosphere.
As used herein, the term xe2x80x9chigh level refrigerationxe2x80x9d means the temperature of refrigeration for the precooler loop is less than 260 K.
As used herein, the term xe2x80x9clow level refrigerationxe2x80x9d means the temperature of the refrigeration for the main loop is less than 240 K.
As used herein, the term xe2x80x9csubcoolingxe2x80x9d means cooling a liquid to be at a temperature lower than that liquid""s saturation temperature for the existing pressure.
As used herein, the term xe2x80x9cwarmingxe2x80x9d means increasing the temperature of a fluid and/or at least partially vaporizing the fluid.
As used herein, the term xe2x80x9ccoolingxe2x80x9d means decreasing the temperature of a fluid and/or at least partially condensing the fluid.
As used herein, the term xe2x80x9cindirect heat exchangexe2x80x9d means the bringing of two fluids into heat exchange relation without any physical contact or intermixing of the fluids with each other.
As used herein, the term xe2x80x9cexpansion devicexe2x80x9d means apparatus for effecting expansion of a fluid.
As used herein, the term xe2x80x9ccompressorxe2x80x9d means apparatus for effecting compression of a fluid.
As used herein, the term xe2x80x9cmulticomponent refrigerant fluidxe2x80x9d means a fluid comprising two or more species and capable of generating refrigeration.
As used herein, the term xe2x80x9crefrigerant fluidxe2x80x9d means a pure component or mixture used as a working fluid in a refrigeration process which undergoes changes in temperature, pressure and possibly phase to absorb heat at a lower temperature and reject it at a higher temperature.
As used herein, the term xe2x80x9cvariable load refrigerantxe2x80x9d means a mixture of two or more components in proportions such that the liquid phase of those components undergoes a continuous and increasing temperature change between the bubble point and the dew point of the mixture. The bubble point of the mixture is the temperature, at a given pressure, wherein the mixture is all in the liquid phase but addition of heat will initiate formation of a vapor phase in equilibrium with the liquid phase. The dew point of the mixture is the temperature, at a given pressure, wherein the mixture is all in the vapor phase but extraction of heat will initiate formation of a liquid phase in equilibrium with the vapor phase. Hence, the temperature region between the bubble point and the dew point of the mixture is the region wherein both liquid and vapor phases coexist in equilibrium. In the preferred practice of this invention the temperature differences between the bubble point and the dew point for a variable load refrigerant generally is at least 10xc2x0 C., preferably at least 20xc2x0 C., and most preferably at least 50xc2x0 C.
As used herein, the term xe2x80x9cazeotropic mixturexe2x80x9d means a mixture of two or more components which act as a single component so that the mixture is totally condensed or totally vaporized at a single temperature, and as the mixture undergoes condensation or vaporization, the concentration of the components in the liquid phase is and remains the same as the concentration of the components in the vapor phase.